The present invention is concerned with hydroelectric generators of the type having a blade arrangement, usually referred to as a runner, mounted on a shaft which rotates the rotor of an electric generator contained within a housing. Water is flowed through a distributor to rotate the runner and thus turn the shaft for the generation of electricity.
Such devices generally comprise a distributor through which water is flowed to impart a tangential momentum to it for impingement upon a runner for rotating the runner and thereby the runner shaft. The runner, which may be encircled by the distributor or positioned immediately downstream of it, is conventionally positioned at the inlet to a draft tube through which the water flows for discharge as tail water downstream of the powerhouse in which the generator is located.
Many dams and powerhouse sites require the provision of a waste water, i.e., overflow water, conduit to accommodate discharge of water in order to control the water level as desired during flood or very high water flow periods. It would be advantageous to generate power from such overflow water by installing a generator in the (or in each) overflow conduit. However, the installation of a hydroelectric generator in such an overflow conduit significantly reduces the maximum flow rate capacity of the conduit because of the constriction of the inlet by positioning of the runner and its associated distributor at the inlet. For smaller generators it may be feasible to simply remove the entire generator, or at least withdraw it from the discharge inlet a distance sufficient to clear the inlet to accommodate higher rates of flow of water through the overflow conduit. However, such removal or repositioning is not feasible for large machines which may weigh 50 tons or more. One solution would be to provide an extra overflow conduit to accommodate flow in excess of that which can be handled by the generator-equipped overflow conduit. However, this involves the expense of constructing a second waste water conduit, equipping the system with necessary flow gates, valving and associated controls, etc. Further, such expedient is usually not feasible in existing installations where a single, large diameter waste water discharge conduit may be available and there is not room sufficient to install a second conduit, or the cost of doing so is prohibitive.
The present invention provides a means for overcoming the aforesaid difficulties.